The major goal in this proposal is to develop an instrument to measure the vibration of the organ of Corti in the living guinea pig. The instrument will use the principles of optical coherence tomography (OCT) and low optical coherence interferometry to visualize the basilar membrane and the internal structures of the organ and to measure their vibratory displacements induced by sound stimulation of the ear, respectively. The OCT interferometer will utilize light from two different super luminescent diodes coupled into a common optical fiber, allowing simultaneous measurement of the vibratory displacement of the basilar membrane and the reticular lamina components of the organ of Corti. The first two aims of the proposal are 1) to develop a dual source (two channels) OCT interferometer for measurements at a single location in the organ and 2) to develop a scanning OCT interferometer to measure organ of Corti motion in three dimensions. OCT interferometry will have the advantage of not requiring any reflective objects (such as mirrors or beads) to be placed on the ear tissues and will have high optical spatial resolution (particularly in the 'z' direction along the optical axis) allowing accurate magnitude and phase measurements of organ of Corti tissue vibration. The third aim is to use the OCT instrument to measure the three-dimensional vibration pattern of the basilar membrane and reticular lamina in the guinea pig. The data will give critical new insight into the micro mechanical motion of the organ of Corti and on the mechanism of the cochlear amplification process whereby outer hair cells are thought to be actively enhancing organ of Corti motion.